Generally known effluent distributing travelling irrigators typically used in New Zealand for the disposal and use as a fertiliser of dairy manure, are coupled to a hydrant in a paddock by means of a long flexible pipe around 200 meters long and 65 mm in diameter. The irrigator has a nozzle boom arm which rotates or oscillates in operation under the force of a jet emitted from the nozzle or nozzles, and as it rotates or oscillates it drives a winch. A cable is attached to this winch and the other end to a solid anchor and as the nozzle arm rotates or oscillates, the winch winds up the cable so that the irrigator pulls itself (and the flexible hose to which it is connected) along the paddock distributing the effluent liquid fertiliser or water etc. In most cases the motion of rotation or oscillation of the nozzle boom arm is transferred to the winch drum by way of mechanical linkages such as cranks or cams and pushrods operating in conjunction with clutches commonly featuring ratchet mechanisms and in some cases the motion is transferred from the rotating nozzle arm to the winch drum by means of a gearbox and chain or belt drive.
It is important that the irrigator speed is controlled so that the application depth of the sprayed liquid is approximately constant over the paddock and this is usually achieved by adjusting the angles by which the jet or jets leave the nozzles relative to the nozzle boom arm assembly. However, as the irrigator travels it will encounter changing gradients and hose drag and perhaps other retarding forces so that the original nozzle boom arm rotational or oscillating speed and torque may no longer be adequate to maintain the desired speed of the irrigator. When this happens the irrigator travel speed will slow down and will not regain its set speed until the retarding forces are again equal to those at which the irrigator travel speed was originally set. In this way the application depth of the liquid issuing from the nozzles will vary according to the varying irrigator travel speed. The present mechanical linkages and/or belt/chain transmissions do not incorporate speed regulation. A further difficulty occurs when the retarding force approaches or exceeds the tensile strength of the cable. In such cases the nozzle boom arm may be able to apply sufficient torque to the winch drum to tension the pulling cable excessively or even to breaking point.